title: Ligand- and drug-binding studies of membrane proteins revealed through circular dichroism spectroscopy.
abstract: A great number of membrane proteins have proven difficult to crystallise for use in X-ray crystallographic structural determination or too complex for NMR structural studies. Circular dichroism (CD) is a fast and relatively easy spectroscopic technique to study protein conformational behaviour. In this review examples of the applications of CD and synchrotron radiation CD (SRCD) to membrane protein ligand binding interaction studies are discussed. The availability of SRCD has been an important advancement in recent progress, most particularly because it can be used to extend the spectral region in the far-UV region (important for increasing the accuracy of secondary structure estimations) and for working with membrane proteins available in only small quantities for which SRCD has facilitated molecular recognition studies. Such studies have been accomplished by probing in the near-UV region the local tertiary structure of aromatic amino acid residues upon addition of chiral or non-chiral ligands using long pathlength cells of small volume capacity. In particular, this review describes the most recent use of the technique in the following areas: to obtain quantitative data on ligand binding (exemplified by the FsrC membrane sensor kinase receptor); to distinguish between functionally similar drugs that exhibit different mechanisms of action towards membrane proteins (exemplified by secretory phospholipase A2); and to identify suitable detergent conditions to observe membrane protein-ligand interactions using stabilised proteins (exemplified by the antiseptic transporter SugE). Finally, the importance of characterising in solution the conformational behaviour and ligand binding properties of proteins in both far- and near-UV regions is discussed. This article is part of a Special Issue entitled: Structural and biophysical characterisation of membrane protein-ligand binding.
authors.affiliation: Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK; School of Biological Sciences, University of Liverpool, Liverpool, UK. Electronic address: giuliano.siligardi@diamond.ac.uk.
authors.forename: Giuliano
authors.initials: G
authors.lastname: Siligardi
authors.forename: Rohanah
authors.initials: R
authors.lastname: Hussain
authors.forename: Simon G
authors.initials: SG
authors.lastname: Patching
authors.forename: Mary K
authors.initials: MK
authors.lastname: Phillips-Jones
mesh_terms: D002942:Circular Dichroism / Q000379:methods*; D008024:Ligands; D008565:Membrane Proteins / Q000378:metabolism*; D009994:Osmolar Concentration; D004364:Pharmaceutical Preparations / Q000378:metabolism*
chemical_list: D008024:Ligands; D008565:Membrane Proteins; D004364:Pharmaceutical Preparations
keywords: 1,2-dimyristoyl-sn-glycero-3-phosphocholine; 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine; CD; Circular dichroism (CD) spectroscopy; DDM; DMPC; DPPE; GBAP; Ligand interactions; Membrane proteins; SRCD; Synchrotron radiation circular dichroism (SRCD); TM; Two-component signal transduction; UV; circular dichroism; dissociation constant; gelatinase biosynthesis-activating pheromone; k(d); k(d) determination; n-dodecyl-β-d-maltoside; synchrotron radiation circular dichroism; transmembrane domain; ultraviolet